The transmission of audio signals in compressed digital packet formats, such as MP3, has revolutionized the process of music distribution. Recent developments in this field have made possible the reception of streaming digital audio with handheld network communication devices, for example. However, with the increase in network traffic, there is often a loss of audio packets because of either congestion or excessive delay in the packet network, such as may occur in a best-effort based IP network.
Under severe conditions, for example, errors resulting from burst packet loss may occur which are beyond the capability of a conventional channel-coding correction method, particularly in wireless networks such as GSM, WCDMA or BLUETOOTH. Under such conditions, sound quality may be improved by the application of an error-concealment algorithm. Error concealment is an important process used to improve the quality of service (QoS) when a compressed audio bit stream is transmitted over an error-prone channel, such as found in mobile network communications and in digital audio broadcasts.
Perceptual audio codecs, such as MPEG-1 Layer III Audio Coding (MP3), as specified in the International Standard ISO/IEC 11172-3 entitled “Information technology of moving pictures and associated audio for digital storage media at up to about 1,5 Mbits/s—Part 3: Audio,” and MPEG-2/4 Advanced Audio Coding (AAC), use frame-wise compression of audio signals, the resulting compressed bit stream then being transmitted over the audio packet network.
One method of decoding and segment-oriented error concealment, as applied to MPEG1 Layer II audio bitstreams, is disclosed in international patent publication WO98/13965. In the reference, decoding is carried out in stages so that the correctness of the current frame is examined and possible errors are concealed using corresponding data of other frames in the window. Detection of errors is based on the allowed values of bit combinations in certain parts of the frame. For an MP3 transmission, the frame length refers to the audio coding frame length, or 576 pulse code modulation (PCM) samples for a frame in one channel. The frame length is approximately thirteen msec for a sampling rate of 44.1 KHz.
Conventional error detection and concealment systems operate with the assumption that the audio signals are stationary. Thus, if the lost or distorted portion of the audio signal includes a short transient signal, such as a ‘beat,’ the conventional system will not be able to recover the signal.
What is needed is an audio data decoding and error concealment system and method which can mitigate the degradation of the audio quality when packet losses occur.
It is an object of the present invention to provide such an audio error concealment system and method which can detect audio transmission errors, and effectively conceal missing or corrupted audio data segments without perceptible distortion to a listener.
It is a further object of the present invention to provide such a method and system audio reception in which the error concealment process uses control input from an enhanced frame error detection and a compressed domain beat detection.
It is a further object of the present invention to provide such a system and method which can recover short, transient signals when lost or distorted.
It is a further object of the present invention to provide a method and device suitable for audio reception in which the process of error concealment utilizes audio frame error detection and replacement.
It is yet another object of the present invention to provide such a device and method in which audio error detection and error concealment resources are efficiently used.
It is another object of the present invention to provide such a device which includes a decoder having enhanced audio frame error detection capability.
It is also an object of the present invention to provide a communication network system incorporating such a device and method in which error concealment is effected by frame replacement of the distorted or corrupted audio data.
Other objects of the invention will be obvious, in part, and, in part, will become apparent when reading the detailed description to follow.